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A novel antibacterial immunostimulant using Platinum nanoparticles (PtNPs) and lectin from Metapenaeus dobsoni (Md-Lec) was developed. The Md-Lec and PtNPs (Pt-lec) hybrid formed through non-covalent interaction exhibits antimicrobial activity against fish specific pathogens by affecting membrane integrity and producing excess reactive oxygen species. The therapeutic efficacy of Pt-lec was demonstrated through rescuing Aeromonas hydrophila infected Nile Tilapia. Pt-lec prevents the infection spreading and reduces the bacterial bioburden in less than 12 h, and as a result of this the fish were restored to normalcy. To assess immunostimulation, we studied the expression of three different immune related genes, namely LEC, Myd88 and COX-2 in the gills, liver, spleen and kidney of fish under various experimental conditions. Our results showed that Pt-lec treatment appeared to be better when compared to lectin alone in enhancing the expression of Myd88 and COX-2, but LEC was not as expected. These results suggest that Pt-lec has the ability to protect Nile Tilapia against bacterial infection by restricting bacterial bioburden through their direct effects on the bacterial membrane and indirectly through their effects on host immune-related gene expression. This hybrid could have potential "green" application in fish farming in rescuing infected animals when compared to widely and unregulated antibiotics.

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Lectins are known for their ability to bind to cell surface glycans, and are useful to develop a glycan-targeted drug delivery system. This study aimed to evaluate the capacity of pectin capped copper sulfide nanoparticles (pCuS NPs) to modulate the antibacterial activity of a lectin, Md-Lec, purified from the shrimp, Metapenaeus dobsoni. Fluorescence spectroscopy revealed that Md-Lec has the ability to form a complex with pCuS NPs. Haemagglutination assay showed that the carbohydrate binding site of the lectin was preserved even after complexing with pCuS. The minimum inhibitory concentrations (MICs) obtained for Md-Lec and pCuS NPs against the tested aquatic pathogens were 50 µg ml-1 and 12.5 µM, respectively. Interestingly, the MIC of Md-Lec-pCuS NPs complex was four fold lower than that of pCuS, which was attributed to the bacterial cell surface glycan recognization activity of Md-Lec. Zone of inhibition assay showed that the zone size was highest for the lectin conjugated nanoparticles. Mechanistic study revealed that Md-Lec-pCuS NPs affect the bacterial membrane integrity and produce a large volume of reactive oxygen species to kill the bacteria. The practical aspect of using this lectin-pCuS NPs complex was evaluated by treating bacteria infected Nile tilapia (Oreochromis niloticus). The bacterial load was much less in the lectin-pCus NPs complex treated fish; moreover, the fish fully recovered from the infection. It was concluded that the conjugate of antibacterial lectin and NPs is more effective than the individual components.

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The study is carried out to understand the antimicrobial and immunological response of a potential immune molecule lectin, MmLec isolated from haemolymph of Speckled shrimp, Metapenaeus monoceros. MmLec was purified using mannose coupled Sepharose CL-4B affinity chromatography, which was further subjected on SDS-PAGE to ascertain the distribution of their molecular weight. Sugar binding specificity assay was conducted at various pH and temperatures to investigate the binding affinity of MmLec towards the specific carbohydrate molecule. Functional analysis of immune molecule MmLec included haemagglutination assays performed using human erythrocytes and yeast agglutination activity against Saccharomyces cerevisiae which, were analyzed using light microscopy. In order to study the antimicrobial activity, two Gram-negative (Vibrio parahaemolyticus and Aeromonas hydrophila) and two Gram-positive (Staphylococcus aureus and Enterococcus faecalis) bacteria were treated with purified MmLec. Moreover, these bacterial species were also treated at different concentration of the MmLec to speculate the antibiofilm properties of MmLec which was analyzed under Light Microscopy and Confocal Laser Scanning Microscopy. In addition, other functional characterization of MmLec showed the uniqueness of MmLec in agglutination of human erythrocyte as well as the cells of yeast Saccharomyces cerevisiae. Also, the phenoloxidase activity and encapsulation assay was evaluated. MTT assay displayed that MmLec are potent in anticancer activity. The study will help to understand the immunological interference and antimicrobial nature of MmLec which would be supportive in establishing a potential therapeutic tool and to develop better and novel disease control strategies in shrimp and farmed aquaculture industries as well as in health management.

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The present study reveals purification and characterization of the lectin from the haemolymph of Metapenaeus dobsoni. The Md-Lec was purified by affinity chromatography with mannose coupled sepharose CL-4B column and it exhibits single band with a molecular weight of 68 kDa in SDS-PAGE. Furthermore, the molecular mass was confirmed by MALDI-TOF and functional groups present were analysed by FTIR. The surface morphology of purified Md-Lec displays the homogeneous nature of protein. The X-ray diffraction (XRD) analysis expresses three peaks at 10.7716̊, 21.6258̊ and 31.7523̊which indicate the crystalline nature of the protein and the retention time of 3.068 min evident from HPLC reveals the purity of the sample. Functional analysis of purified Md-Lec exhibits yeast agglutination activity against Saccharomyces cerevisiae and has the ability to agglutinate the human erythrocytes, which was observed by light microscopy. It also exhibited phenoloxidase activation, encapsulation and phagocytic activities. In addition, purified Md-Lec showed the broad spectrum of bacterial agglutination activity against Gram negative Vibrio parahaemolyticus and Aeromonas hydrophila, important fish pathogens. Antiviral potential and anticancer activity of purified Md-Lec against CyHV-2 virus and MDA-MB-231 breast cancer cell lines were also evaluated in this study.

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The present study reveals purification and characterization of a C-type lectin from the serum of pearl spot, Etroplus suratensis (Es-Lec). The Es-Lec was purified by affinity chromatography with mannose coupled sepharose CL-4B column and it exhibits single band with a molecular weight of 75 kDa in SDS-PAGE. The surface morphology of purified Es-Lec displays the homogeneous nature of protein. A distinct peak with a retention time of 2.958 min was appeared in high performance liquid chromatography (HPLC), X-ray diffraction (XRD) analysis expresses a single peak at 31.8372̊ and MALDI-TOF peaks which shows the purity and crystalline nature of the protein respectively. Functional analysis of purified Es-Lec exhibits yeast agglutination activity against Saccharomyces cerevisiae and has the ability to agglutinate the human erythrocytes, which was observed by light microscopy and haemagglutination inhibition was also done. In addition, purified Es-Lec showed the broad spectrum of antibacterial activity against Gram negative Vibrio parahaemolyticus and Aeromonas hydrophila. Antibiofilm potential of purified Es-Lec against selected Gram-negative bacteria exhibited the disruption of biofilm architecture at the concentration of 50 µg ml-1 and also it exhibited antiviral and anticancer activity.

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